1. Field of the Invention
This invention relates to a process and apparatus for dissipating the energy of a pressurized stream as that stream traverses a pressure control valve, and more particularly, to dissipating the energy of a wet oxidation mixture after that stream traverses a pressure control valve.
2. Description of Related Art
Wet oxidation is a well known process for treatment of aqueous wastewaters. The process involves heating a mixture of the wastewater plus an oxygen-containing gas to elevated temperature and pressure to effect oxidation of oxidizable substances contained in the wastewater. All wet oxidation systems include one or more pressure control valves to regulate the flow of liquid, solids and gases from the high pressure part of the system to the low pressure part of the system. Depending on the composition of the process stream and the temperature and pressure of the flowing stream, the pressure control valve discharge can be highly abrasive to the piping and receiving vessel on the low pressure side. The process stream velocity is commonly at or close to sonic velocity due to the high pressure drop across the pressure control valve. There will be steam flashing at the control valve outlet if the process stream temperature is close to the vapor pressure of water. The wet oxidation system process stream commonly contains significant concentrations of suspended solids. The combination of suspended solids, flashing steam, and high velocity makes the pressure control valve effluent extremely abrasive.
Presently, a specially designed pressure control valve and receiving pot combination are employed to minimize the effects of abrasion on the low pressure side of the system. The receiving pot is typically small in diameter and includes special wear resistant materials that can stand up to highly abrasive conditions for long periods of time. The total process stream sweeps through the receiving pot and on to a standard phase separator vessel. It is difficult to determine the correct size for a receiving pot and there are still applications where the current pot design fails due to unknown and/or uncontrollable process factors.
Ledding, in U.S. Pat. No. 3,150,105, discloses a blow down tank or other suitable decompression vessel which receives the cooled regenerated carbon slurry from a wet oxidation reactor. No further description of the blow down tank is provided.
In U.S. Pat. No. 3,994,702, Schweimanns et al. disclose a flooded slucing chamber for ash removal from a pressurized gasification chamber.
Meidl et al., in U.S. Pat. No. 4,620,563 disclose a blowdown pot with an inlet pressure control valve through which the pot receives unwanted residue e.g., ash from a high pressure chemical reactor. This reactor residue can be continuously or semi-continuously blown out from the high pressure, high temperature chemical reactor into the relatively low pressure blowdown pot which includes means for maintaining a liquid level therein, thus minimizing steam flashing and vessel wear.
In U.S. Pat. No. 5,011,114, Depuydt et al. disclose a pressure control valve with a valve seat and support assembly which extends beyond the valve body to prevent erosion by the blowdown slurry. The apparatus also includes a displacement-compensating seal between the valve and receiving vessel to allow for thermal expansion and contraction during the blowdown cycle while maintaining the integrity of the seal.
In general, these references disclose methods and/or apparatus for handling only a fraction of the total process stream passing through a wet oxidation treatment system. The receiving pot presently in use is susceptible to failure due to abrasion wear. Applicants have devised a process and an apparatus to overcome the shortcomings of the process and apparatus presently in use.